In recent years, a development of handhold communication gadgets is remarkable. Especially, downsizing and reduction in weight of mobile phones have advanced. Further, with respect to also various electronic equipments such as video camera (handy camera or the like), codeless phone, lap-top personal computer (notebook type personal computer) other than the mobile phone, such the downsizing and reduction in weight have been also advanced.
Since these electronic equipments are provided with a secondary battery to an electronic equipment body, the electronic equipments can be available without plugging in, so that a portability and convenience have been greatly improved. At the present time, a capacity of the secondary is limited to some extent, so that the secondary battery is necessary to be performed with a power-charging operation at least once every several days to several weeks.
As a power charging method, there are two types of charging methods: a contact-type charging system; and a non-contact type charging system. The contact-type charging system is a system in which an electrode of a power receiving apparatus and an electrode of a power supplying apparatus are directly contacted to each other thereby to perform the power charging. The contact-type charging system has a simple structure for constituting the apparatus, so that the contact-type charging system has been generally adopted in wide application field.
However, in accordance with the progress of the downsizing and reduction in weight of the electronic equipments in recent years, there has been posed problems such that a weight of each electronic equipments is reduced, so that a contact pressure between the electrode of the power receiving apparatus and the electrode of the power supplying apparatus becomes insufficient thereby to cause a charging defect (charging fault). Further, the secondary batter has a small resistance to heat, so that it is necessary to avoid a temperature rise of the secondary battery, and a circuit design requires to be carefully performed so as not to cause an over discharge and an overcharge. In order to cope with these problems, the non-contact type charging system has been reviewed in these days.
The non-contact type charging system is a power charging system utilizing an electromagnetic induction caused by coils provided to both the power receiving apparatus and the power supplying apparatus. In this type of the charging system, due to the non-contact type, there is no need to pay attention to the contact pressure between the electrodes of the two apparatuses. Further, it is unnecessary to pay attention to the contact pressure, so that a stable charging voltage can be supplied without being influenced by the contacting state of the electrodes of the apparatuses.
The conventional non-contact type charging system has been used for electronic equipments such as electric toothbrush, electric shaver or the like that are driven by a low power consumption and require a long charging time. As the secondary battery at that time, a nickel-hydrogen battery is mainly used, so that most of the nickel-hydrogen batteries require a long charging time of about 8 hours. In recent years, as a novel secondary battery, a high capacity and high density batteries such as lithium-ion secondary battery or the like have come into existence. As a result, with respect to the electronic equipments such as mobile phone, personal computer or the like that are driven by a high power consumption and require a rapid charging operation, the non-contact type charging system has been eagerly reviewed in these days.
As one example of the non-contact type charging apparatus, there have been proposed systems in Japanese Unexamined Patent Application Publication No. 11-265814 (Patent Document 1) or Japanese Unexamined Patent Application Publication No. 2000-23393 (Patent Document 2). Both systems adopt a structure in which a ferrite core is used as a magnetic core and a coil is wound around the magnetic core thereby to realize the apparatus which is reduced in size.
Further, in the charging apparatus disclosed in Japanese Unexamined Patent Application Publication No. 9-190938 (Patent Document 3), ferrite powder and amorphous powder are mixed thereby to form a resin substrate and a coil or the like is mounted on the resin substrate thereby to realize the charging apparatus reduced in size and thickness.
However, when ferrite is worked to be thin shape, the thin ferrite becomes brittle and has a low impact resistance, so that there has been posed a problem such that the power receiving system turns out to be defective due to a dropping or collision or the like of the apparatus. Further, in order to reduce a size in thickness of a power receiving portion so as to correspond to the reduction in thickness of the electronic equipment, there has been adopted a planar coil which is formed by printing a metal powder paste onto a coil. As one example of structure for strengthening bondage by using the planar coil and a magnetic sheet, there have been proposed the structures disclosed in Japanese Unexamined Utility Model Application Publication No. 58-80753 (Patent Document 4), Japanese Unexamined Patent Application Publication No. 4-122007 (Patent Document 5) or Japanese Unexamined Patent Application Publication No. 8-148360 (Patent Document 6). In these proposed structures, a magnetic body (magnetic sheet) is used as a core material for strengthening the bondage between a primary coil and a secondary coil.
On the other hand, when an electric transmission rate is increased to be large, defects due to heat generation are liable to occur at portions not only the bondage between adjacent transformers but also peripheral parts of the transformers. That is, in a case where the planar coil is used, a magnetic flux passing through the planar coil is interlinked to a substrate or the like provided inside the equipment, so that a temperature of an inside of the apparatus is increased to generate heat due to eddy current caused by electromagnetic induction. As a result, there has been posed a problem such that high electric power cannot be transmitted and it takes long time to charge the electricity.
To cope with this problem, the magnetic body (magnetic sheet) is used as also a shielding member with respect to a rear surface. In order to obtain a sufficient shielding effect, it has been considered that if the magnetic body (magnetic sheet) has the larger magnetic permeability or the wider area or the larger thickness, the more effective shielding effect can be obtained.
Further, in order to increase the electric transmission rate, it is required to increase the electric power. However, when the electric transmission is continued to a metallic body, the metallic body generates heat due to the eddy current caused in the metallic body. Therefore, it is necessary to provide the following safety system. For example, in a case where a coil of a power transmitting (power supplying) apparatus is a primary coil while a coil of a power receiving apparatus is a secondary coil and the primary coil is used as an antenna of RF-ID tag (radio-frequency-identification tag), the safety system judges whether or not the secondary coil exists at upper portion of the primary coil on the basis of a RF signal.
However, in this case, when inductance of the primary coil is greatly changed in accordance with a positional relationship between the magnetic body (magnetic sheet) and the coil of the power transmitting apparatus side, a resonant frequency of a resonant circuit provided to a side of the primary coil for power transmitting is also greatly varied, so that there has been caused defects such that a sufficient resonance cannot be obtained and the above antenna cannot function well.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-265814    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-23393    Patent Document 3: Japanese Unexamined Patent Application Publication No. 9-190938    Patent Document 4: Japanese Unexamined Utility Model Application Publication No. 58-80753    Patent Document 5: Japanese Unexamined Patent Application Publication No. 4-122007    Patent Document 6: Japanese Unexamined Patent Application Publication No. 8-148360